Nalley Valley project on schedule

The small army of construction workers reconfiguring the snarl of freeway lanes over Tacoma's Nalley Valley will stay home this week.

Most workers are in the midst of a 10-day holiday vacation that started Christmas Eve. It’s only their second extended break since the highway construction project began two years ago.

Atkinson Construction, the prime contractor, is pausing with most of the heavy lifting done on the first phase of the project and the end clearly in sight. Work started on the $183 million initial phase Jan. 5, 2009.

“We’re on schedule to deliver this summer,” said Jon Deffenbacher, the state Department of Transportation’s project engineer.

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The first phase consists primarily of connecting traffic on Interstate 5 with westbound state Route 16, heading toward the Tacoma Narrows bridges.

Stage two, scheduled to begin next year and continue through 2013, will cost $124 million and complete the realignment for traffic eastbound on SR 16.

Together, the two phases will comprise one of the most complex freeway intersections in Washington, according to Deffenbacher.

Beyond that, WSDOT plans to incorporate high-occupancy vehicle lanes in the interchange, a $213 million revamp that, at this point, is to take place from 2020 to 2022.

The centerpiece of the first phase has been a 1,060-foot-long, curved bridge, vaulting over I-5 and Nalley Valley.

The bridge, a “balanced, cantilever segmental” design, is a first for the Transportation Department. It was pieced together in midair by lifting 112 vertebrae-shaped concrete sections, built off site in Tacoma and trucked to the job.

All the segments are in place, cantilevered and balanced on concrete columns.

When workers return next week, they’ll continue aligning and filling in the last remaining 2- to 4-foot-wide gaps between cantilevered sections.

They’ll also continue laying down the final roadway surface – 71/2 inches of concrete – and pouring the traffic barriers at the edges of the roadways.

So far, said WSDOT spokeswoman Claudia Cornish, the final roadway surfacing has been completed on 30 of the 47 spans of bridge decks, and barriers have been poured on 20 of the 47 spans (about 4,200 linear feet).

One of the biggest tasks still coming up in the next few months, Deffenbacher said, is building the approach to the new bridge along the northbound lanes of I-5.

That merging point will replace the old, road-rage inspiring alignment that funneled northbound vehicles on I-5 heading for SR 16 into a single lane, then merged them with traffic exiting from I-5’s southbound lane in a quick, dangerous weave to the old exit at Sprague Avenue.

Accomplishing that transition without interrupting the heavy flow of I-5 will take some serious effort, Deffenbacher said.

“It will be a big impact piece of work,” he said.

The plan calls for taking vehicles bound for SR 16 off northbound I-5 and onto a new, temporary roadway. Once the vehicles are out of the way, the contractor will grade and fill for the new approach.

The temporary roadway will be in use for 21/2 to 3 months, Deffenbacher said.

‘SIMPLER AND SAFER’

If completing the cantilevered bridge was the high point of Phase One construction, the low point no doubt was the expensive and embarrassing misalignment of an exit ramp from SR 16 to Sprague Avenue.

The error made it necessary to tear out and reconstruct 700 feet of the ramp, at a cost of $890,000, plus $45,000 in labor costs.

The mistake did not delay the project, according to WSDOT, because the repair took place concurrently with other work. The cost came out of a portion of the budget designated for contingencies.

Last week, in a construction trailer beneath the partially completed Nalley Valley viaduct, Deffenbacher laid out a poster-sized plan of the finished project from an aerial perspective.

Seen that way, the interwoven freeways, onramps and exits look like a badly snarled fishing line.

That’s not how it will appear to drivers who use it, Deffenbacher promised. For them, he said, it will be well-marked and easily negotiated.

“When you look at it on paper, it’s very complex,” he said, “but the purpose is to make it simpler and safer for drivers.”